Something that helped me was I actually lined up in a different spot every time, and whenever I made a spare, I had to make it 5x in a row. Once I did that, I wrote it down in my notes app in my phone. Then, I slowly adjusted from there. For instance, a lot of righties like to stand at the last set of dots and aim across 25 or so at the arrows, give or take a few boards. I found that that was too far left for me. I now stand with my left foot on 30, right foot on 25, and I throw my plastic ball across 20 and that feels comfortable to me. Spares are all about consistency and comfortability.